There is a continuing need for improvements in shredders for reducing scrap metal materials, especially scrapped automobiles, into convenient size pieces for use in steel mills. Such shredders have been known for a long time but there are basic problems that have never been solved. One problem is how to reduce the scrap metal material to the desired size pieces with a minimum consumption of energy. Another problem is how to get the maximum use from the shredder components such as grates and to reduce the downtime involved in replacing worn or broken components.
In the past, a variety of attempts have been made to solve these problems including designing shredders with more efficient and durable rotors and hammers and different shaped housings. However, such attempts have not been completely successful.
Representative of a type of shredder which is now widely used is that shown and described in the Newell U.S. Pat. No. 3,482,788. Although the performance of the Newell-type shredder can be improved by employing therein the improved four-arm rotor design and the protective arm caps shown in the Francis U.S. Pat. No. 3,727,848, the energy consumption of the Newell-type shredder is still higher than desired and the internal surfaces of the housing and the grate appear to wear excessively and unevenly.